EP0477087A1 - Device for processing a signal originating from a sensor having a differentiating response - Google Patents

Abstract

The field of the invention is devices for measuring signals in the area of broad-band phenomena. …<??>More precisely, the present invention relates to a device for processing an electrical signal originating from a sensor (10) having a differentiating response, the sensor being designed for the measurement of an electric or magnetic field, surface charging currents or other derived quantities. The processing includes the calculation of the primitive (indefinite integral) of that part of the said signal of spectral frequency which is higher than a low frequency f1. The said device consists of: … …  -a circuit (20) for electronic integration of the said signal from a frequency f2 greater than the said low frequency f1; …  -a compensation circuit (21) amplifying and integrating the said signal between the frequencies f1 and f2. … …<IMAGE>…

Description

The field of the invention is that of signal measurement devices in the field of broadband phenomena.

More specifically, the present invention relates to a device for processing signals originating in particular from nuclear electromagnetic pulse (EMI), lightning or electromagnetic compatibility (EMC) sensors. Such sensors can consist of wideband sensors of electric, magnetic fields, currents or surface charges, having a frequency response ranging from 10 to 100 kHz approximately to more than 1 GHz.

In known manner, these sensors can be either passive sensors or active sensors.

Passive sensors use sensing elements connected to a low impedance load, for example 50 Ω.

The connection between the sensor and the load is usually made by a cable of the same impedance. The operating principle of passive sensors is for example described in the article "Sensors for electromagnetic pulse measurements both inside and away from nuclear source regions" ("Sensors for the measurement of electromagnetic pulses simultaneously inside and away from nuclear sources "), (Carl BAUM, Edward BREEN, Joseph GILLES, John O'NEILL, Gary SOWER, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, Vol. AP-26, n ° 1, January 1978).

Such passive sensors have a derivative response which requires processing to obtain the actual shape of the signal to be measured. The processing consists in integrating the signal coming from the sensor, for example using an RC cell, and in amplifying the integrated signal thanks to an amplifier of input impedance higher than the equivalent impedance of the integrator.

The main advantage of passive sensors is that they allow the passage of high frequencies, up to 10 GHz. In addition, passive sensors are simple to produce. However, such sensors have the disadvantage of being reduced sensitivity.

Active sensors, on the other hand, have a magnetic field and electric field sensitivity of up to 100 and 3000 times respectively greater than passive sensors.

Such active sensors are for example described in the document "Computer-assisted control of EMP measurement on major systems" ("Computer-assisted control for the measurement of electromagnetic pulses on main systems"), Grégoire EUMURIAN, Proceedings of the 6th symposium on Electromagnetic Compatibility, Zurich 1985.

The processing of signals from an active sensor measuring electric fields is ensured by an amplifier with very high impedance (> 1 MΩ), and by a high impedance coil with magnetic core for an active magnetic field sensor.

Active sensors are well suited for applications up to 200 to 300 MHz, but their internal electronics become difficult to carry out beyond.

Furthermore, this electronics leads to more bulky sensors which is contradictory with the increase in frequency and therefore the decrease in the wavelength.

The present invention aims in particular to overcome the drawbacks of existing devices.

More specifically, a first objective of the present invention is to provide a device for processing information supplied by a broadband passive sensor, in particular intended for detecting an electric, magnetic field, a current or a surface charge, making it possible to obtain a sensitivity comparable to that of active sensors, while preserving the bandwidth of the passive sensor.

An additional objective of the present invention is that such a device is simple to produce and has low noise.

• des moyens d'intégration électronique dudit signal, à partir d'une fréquence f₂ supérieure à ladite fréquence basse f₁ ;
• des moyens de compensation amplifiant et intégrant ledit signal entre les fréquences f₁ et f₂.

These objectives, as well as others which will appear subsequently, are achieved by means of a device for processing an electrical signal coming from a sensor of the derivative type intended for measuring an electric or magnetic field, currents or surface charge. or other derived quantities, said processing including the calculation of the primitive of the spectral part of said signal of frequency greater than a low frequency f₁, the device comprising:

• means of electronic integration of said signal, from a frequency f₂ higher than said low frequency f₁;
• compensation means amplifying and integrating said signal between the frequencies f₁ and f₂.

Preferably, said compensation means are mounted in line and downstream from said integration means.

Advantageously, said compensation means have an integration slope equal to that of said integration means.

Preferably, said integration slopes are -6dB / octave.

According to a preferred embodiment, said integration means each consist of at least one RC cell.

Advantageously, the device also comprises a high-pass filter in said processing chain, with a cutoff frequency f₀ less than f₁.

Preferably, the slope of the transfer characteristic of said high-pass filter is + 6dB / octave.

According to a preferred embodiment of the present invention, said low frequency f₁ is of the order of 100 kHz and said frequency f₂ of the order of 10 MHz.

Advantageously, said compensation means comprise at least one broadband amplifier and / or at least one transistor.

The device according to the invention is preferably used for processing signals from an electric field, magnetic field, current and / or surface charge sensor.

• la figure 1 représente un capteur passif standard associé à un intégrateur et à un amplificateur, selon un mode de réalisation connu ;
• la figure 2 représente un mode de réalisation avantageux de la présente invention utilisant un capteur passif standard associé à un intégrateur et à un module de compensation ;
• la figure 3 représente la réponse en fréquence du module de compensation de la figure 2 ;
• la figure 4 représente la caractéristique de transfert d'un autre mode de réalisation de la présente invention ;
• les figures 5 et 6 représentent chacune un exemple de réalisation du dispositif selon la présente invention.

Other characteristics and advantages of the present invention will appear on reading the following description of a preferred embodiment of the present invention, given by way of explanation and not limitation, and the appended drawings in which:

• FIG. 1 represents a standard passive sensor associated with an integrator and an amplifier, according to a known embodiment;
• FIG. 2 represents an advantageous embodiment of the present invention using a standard passive sensor associated with an integrator and a compensation module;
• FIG. 3 represents the frequency response of the compensation module of FIG. 2;
• Figure 4 shows the transfer characteristic of another embodiment of the present invention;
• Figures 5 and 6 each show an embodiment of the device according to the present invention.

FIG. 1 represents a standard passive sensor associated with an integrator and an amplifier, according to a known embodiment.

The embodiment shown comprises a sensor 10 connected to a load 12 of impedance R _c through a cable 11 of the same impedance.

The sensor 10 may in particular consist of an electric field, magnetic field, current, surface charge or other derived quantity sensor. It presents a derivative response which it is therefore necessary to integrate to obtain the measured value.

avec:

R_c

: impédance de la charge,

Aeq

: surface équivalente du capteur,

ε₀

= 10⁻⁹/36π

E

: champ électrique

By way of example, for an electric field sensor, the voltage delivered across the terminals of the load R _c is: $${\text{V = R}}_{\text{vs}}\text{Aeq ε₀ dE / dt}$$

with:

R _c

: load impedance,

Aeq

: equivalent sensor area,

ε₀

= 10⁻⁹ / 36π

E

: electric field

The signal from the sensor 10 is integrated by integration means 13, which may in particular consist of an R₁C₁ cell. The integration carried out makes it possible to obtain the value of the signal measured by the derivative sensor 10.

The integrated signal can be followed by an amplifier 14 whose input impedance is large compared to that of the integrator 13 (R _input >> R₁).

avec
   τ₁= R₁C₁ = constante de temps de l'intégrateur 13,
   G = gain de l'amplificateur 14.The output voltage V _s of the amplifier 14 is given by the relation: $${\text{V}}_{\text{s}}{\text{= GR}}_{\text{vs}}\text{Aeq ε₀}\frac{\text{of}}{\text{dt}}\text{x}\frac{\text{1}}{\text{1 + R₁C₁p}}{\text{≈ GR}}_{\text{vs}}\text{Aeq ε₀}\frac{\text{of}}{\text{dt}}\text{x}\frac{\text{1}}{\text{R₁C₁p}}{\text{= GR}}_{\text{vs}}\text{Aeq ε₀}\frac{\text{E}}{\text{τ₁}}$$

with
τ₁ = R₁C₁ = time constant of the integrator 13,
G = gain of amplifier 14.

   avec : H : champ magnétique $$\text{µ = 4π x 10⁻⁷}$$

In the case of a magnetic field sensor, the relationship giving the voltage at the output of the amplifier is: $${\text{V}}_{\text{s}}\text{= G Aeq µoH / τ₁}$$

with: H: magnetic field $$\text{µ = 4π x 10⁻⁷}$$

Integration is carried out from the frequency f₁ = 1 / 2π R₁C₁ where R₁C₁ = τ₁

FIG. 2 represents an advantageous embodiment of the present invention using a standard passive sensor associated with an integrator and a compensation module;

A standard passive sensor 10 is connected to a load resistor of 12 of value R _c through a cable 11 of impedance R _c .

The signal received is processed by a device 22 comprising integration means 20 and compensation means 21.

The integration means 20 can in particular consist of an R₂C₂ cell of the low-pass type. One of the characteristics of the invention is that the time constant τ₂ equal to R₂C₂ is much less than the time constant τ₁ of the known embodiment described in FIG. 1.
We thus have: $$\text{f₂ = 1 / (2π R₂-C₂) ”f₁}$$

Integration from the frequency f₂ higher than the frequency f₁ leads to a sensitivity of the device f₂ / f₁ times greater. The low cut-off frequency has however gone from f₁ to f₂ and the signals coming from the derivative sensor 10 can no longer be integrated from the frequency f₁.

This is why, the integration means 20 are followed by an amplifier 21, constituting compensation means, having a particular response, for compensate for the loss of response at low frequencies. Of course, the amplifier 21 can also be located upstream of the integration means 20.

FIG. 3 represents the frequency response of the amplifier 21.

• Une réponse plate de gain G. f₂/f₁ de 0 à f₁.
• Une pente de -6 dB/octave de f₁ à f₂.
• Une réponse plate de gain G à partir de f₂.

Amplifier 21 has:

• A flat gain response G. f₂ / f₁ from 0 to f₁.
• A slope of -6 dB / octave from f₁ to f₂.
• A flat gain response G from f₂.

This integration system with a low time constant τ₂ followed by compensation of the low frequencies allows a considerable gain in sensitivity without sacrificing the response at low frequencies.

This gain is due to the fact that the conventional integration τ₁ = R₁C₁ (fig. 1) makes it possible to obtain a good response at low frequencies at the cost of a significant reduction in the sensor signal, while the proposed solution makes it possible to gain a factor important on the signal from the sensor at the cost of a slight increase in noise. Indeed, the integration constant τ₂ being low, the amplitude of the signal at the output of the integrator 20 remains high until f₂. The signal / noise ratio of the device in FIG. 2 is therefore higher than that of the assembly in FIG. 1.

This slight increase is produced by the increase in gain in the area f₁-f₂.

The following two examples are used to assess the gain in sensitivity for an electric field sensor and a magnetic field sensor.

A surface electric field sensor Aeq = 10 ⁻²m² connected to a load resistance R _c = 50 Ω is used in combination with a conventional treatment device (fig. 1) then with a device according to the present invention (fig. 2) .

Processing devices must provide a flat response from 100 kHz to 1 GHz.

The classic solution (fig. 1) is to integrate the signal from the sensor from 100 kHz.

or τ_c = 1/ 2π f_c et donc pour f_c = 100 KHz, τ_c = 1,6 µs.For a noise of around 100 µVeff at the input of the amplifier 14 with gain G = 1, we have: $${\text{V}}_{\text{s}}{\text{= R}}_{\text{vs}}{\text{Aeq ε₀ E / τ}}_{\text{vs}}$$

or τ _c = 1 / 2π f _c and therefore for f _c = 100 KHz, τ _c = 1.6 µs.

The noise at the device output is therefore: $${\text{E}}_{\text{noise}}\text{=}\frac{{\text{V}}_{\text{noise}}{\text{x τ}}_{\text{vs}}}{{\text{R}}_{\text{vs}}\text{Aeq ε₀}}\text{=}\frac{\text{100 x 10⁻⁶ x 1.6 x 10⁻⁶}}{\text{50 x 10⁻² <figure-callout id="10" label="x" filenames="imgf0001.png,imgf0002.png" state="{{state}}">x</figure-callout> 10⁻⁹ / 36 π}}\text{= 36 Veff / m}$$

According to the invention (FIG. 2), the signal leaving the sensor is integrated from 10 MHz and the compensation is carried out from 100 kHz to 10 MHz.

The noise in the 10 MHz - 1 GHz band is unchanged and is equal to 100 µVeff.

et pour un filtre à - 6dB/octave (premier ordre) : $${\text{1 µVeff. (π/2)}}^{\text{½}}\text{= 1,25 µVeff}$$

The noise in the 100 kHz - 10 MHz band is, for a perfect filter: $${\text{100 µVeff. (100 KHz / 1 GHz)}}^{\text{½}}\text{= 1 µVeff}$$

and for a filter at - 6dB / octave (first order): $${\text{1 µVeff. (π / 2)}}^{\text{½}}\text{= 1.25 µVeff}$$

Il se trouve donc à l'entrée: $$\text{1,25 . 100 = 125 µVeff}$$

Le bruit total à l'entrée est de: $${\text{(100² + 125²)}}^{\text{½}}\text{= 160 µVeff}$$

Le bruit en champ électrique devient : $${\text{E}}_{\text{bruit}}\text{=}\frac{\text{160 x 10⁻⁶ x 1,6 x 10⁻⁸}}{\text{50 x 10⁻² x 10⁻⁹/36 π}}\text{= 0,58 Veff/m}$$

This noise is amplified with an additional gain of $$\text{10 MHz / 100 kHz = 100}$$

It is therefore located at the entrance: $$\text{1.25. 100 = 125 µVeff}$$

The total noise at the entrance is: $${\text{(100² + 125²)}}^{\text{½}}\text{= 160 µVeff}$$

The noise in the electric field becomes: $${\text{E}}_{\text{noise}}\text{=}\frac{\text{160 x 10⁻⁶ x 1.6 x 10⁻⁸}}{\text{50 x 10⁻² <figure-callout id="10" label="x" filenames="imgf0001.png,imgf0002.png" state="{{state}}">x</figure-callout> 10⁻⁹ / 36 π}}\text{= 0.58 Veff / m}$$

The noise therefore dropped by 36 dB.

According to another embodiment, a magnetic field sensor of equivalent surface Aeq = 10⁻³m² and R _c = 50 Ω is used in combination with a conventional treatment device (Figure 1) then in combination with device according to the present invention (fig. 2).

A flat response is desired from 100 kHz to 1 GHz.

pour f_c= 100 kHz, τ_c = 1,6 µs, d'où: $${\text{H}}_{\text{bruit}}\text{=}\frac{{\text{V}}_{\text{bruit}}{\text{x τ}}_{\text{c}}}{\text{Aeq µ₀}}\text{=}\frac{\text{100 x 10⁻⁶ x 1,6 x 10⁻⁶}}{\text{10⁻³ x 4π10⁻⁷}}\text{= 127 mA/m}$$

The classic solution (fig.1) is to integrate the signal from the derivative sensor from 100 kHz. For a unit gain of the amplifier 14, the output voltage V _s of the device is equal to: $${\text{V}}_{\text{s}}{\text{= Aeq µ₀H / τ}}_{\text{vs}}{\text{with V}}_{\text{noise}}\text{= 100 µVeff}$$

for f _c = 100 kHz, τ _c = 1.6 µs, hence: $${\text{H}}_{\text{noise}}\text{=}\frac{{\text{V}}_{\text{noise}}{\text{x τ}}_{\text{vs}}}{\text{Aeq µ₀}}\text{=}\frac{\text{100 x 10⁻⁶ x 1.6 x 10⁻⁶}}{\text{10⁻³ x 4π10⁻⁷}}\text{= 127 mA / m}$$

According to the invention, the integration is carried out from 10 MHz and the compensation from 100 kHz to 10 MHz.

The total noise reduced to the input is 160 µVeff. $${\text{H}}_{\text{noise}}\text{= 127 mAeff x}\frac{\text{160}}{\text{100}}\text{x}\frac{\text{1}}{\text{100}}\text{= 2 mAeff / m}$$

The same gain in sensitivity as with an electric field sensor is obtained.

Figure 4 shows the frequency response of another embodiment of the present invention.

The frequency zone 0 to f₁ is not used by the device according to the invention. On the other hand, it produces noise which it is possible to limit by placing in the processing chain a high-pass filter with cut-off frequency f₀, with f₀ less than f₁. Such a filter can be placed before or after the integration means 20 (FIG. 2) or else at the output of the compensation means 21.

The transfer function of FIG. 4 is that of a high-pass filter combined with the compensation means 21.

If the integration means 20 are also taken into account, the transfer function is that shown in dotted lines starting at f₂.

For the two examples mentioned above, a high-pass filter with a cut-off frequency of 75 kHz makes it possible to reduce the low-frequency noise from 125 µVeff to: 125 (25/100) ^½ = 62.5 µVeff (f₁ - f₀ = 100 - 75 = 25 kHz), i.e. a gain of 2.6 dB.

The transfer function shown in Figure 4 is that obtained with a first order high pass filter, but it is of course possible to use a higher order filter.

Figures 5 and 6 each show an embodiment of the device according to the present invention.

FIG. 5 represents a first advantageous embodiment of the device according to the present invention.

The device shown constitutes a chain for processing a signal from a derivative sensor 10. Cell 20 constitutes a cutoff frequency integrator f₂ = 1 / 2π R₂C₂.

Cell 20 is followed by an amplifier 50 with an input impedance much higher than the equivalent impedance of cell 20. Amplifier 50 has a higher gain than the ratio f₂ / f₁.

A capacitor C connected in series at the output of the amplifier 50 makes it possible to limit the passband frequency band below f₁ and thus further reduce the noise.

avec $$\text{ω₁ = 1 / (R₃ + R₄)C₃ = 2π.f₁}$$

$$\text{ω₂ = 1 / R₄C₃ = 2π.f₂}$$

Il est ainsi possible de régler indépendemment les fréquences de coupure f₁ et f₂ du filtre.The capacitor C is followed by a filter R₃ R₄ C₃ with transfer function: $$\text{T (p) = R₄ (p + ω₂) / (R₃ + R₄) (p + ω₁)}$$

with $$\text{ω₁ = 1 / (R₃ + R₄) C₃ = 2π.f₁}$$

$$\text{ω₂ = 1 / R₄C₃ = 2π.f₂}$$

It is thus possible to independently adjust the cutoff frequencies f₁ and f₂ of the filter.

The filter R₃ R₄ C₃ is followed by an amplifier 51 having an input impedance much greater than the equivalent impedance of the filter.

Amplifiers 50 and 51 are advantageously broadband amplifiers, but any other type of amplifier is also suitable.

FIG. 6 shows another advantageous embodiment of the device according to the present invention.

For reasons of clarity, the polarization resistors of the transistors T₁ to T₃ have not been shown.

The transistors T₁ and T₃ are mounted in a common collector and thus fulfill a follower function (impedance matching).

The compensation means are constituted by the transistor T₂ and by the network R₃R₄C₃.

avec ω₁= 1/C₃ (R₃ + R₄) et ω₂ = 1/(R₄ C₃)The gain of transistor T₂ is given by the relation: $$\text{Av =}\frac{\text{R₃ R₄}}{\text{R₃ + R₄}}\text{x}\frac{\text{1}}{{\text{R}}_{\text{E}}}\frac{\text{p +}\frac{\text{1}}{\text{R₄ C₃}}}{\text{p +}\frac{\text{1}}{\text{C₃ (R₃ + R₄)}}}\text{=}\frac{\text{R₃ R₄}}{{\text{(R₃ + R₄) R}}_{\text{E}}}\frac{\text{p + ω₂}}{\text{p + ω₁}}$$

with ω₁ = 1 / C₃ (R₃ + R₄) and ω₂ = 1 / (R₄ C₃)

The two capacitors C make it possible to limit the band below f₁ and thus further reduce the noise.

Of course, FIGS. 5 and 6 represent only two preferred embodiments of the present invention, this device for processing the signal from a derivative sensor can be produced in different ways.

In addition, the transfer characteristic of the device may have greater slopes, and in particular of - 12 dB / octave.

Claims (11)

Device for processing an electrical signal from a derivative type sensor (10) intended to measure an electric or magnetic field, surface charge currents or other derived quantities, said processing including the calculation of the primitive of the part of said signal of spectral frequency greater than a low frequency f₁, characterized in that it comprises: - Means (20) for electronic integration of said signal, from a frequency f₂ greater than said low frequency f₁; - compensation means (21) amplifying and integrating said signal between the frequencies f₁ and f₂. Device according to claim 1 characterized in that said compensation means (21) are mounted in line and downstream of said integration means (20). Device according to either of Claims 1 and 2, characterized in that the said compensation means (21) have an integration slope equal to that of the said integration means (20). Device according to any one of Claims 1 to 3, characterized in that the said integration slopes are -6dB / octave. Device according to any one of Claims 1 to 3, characterized in that the said integration means (20) each consist of at least one RC cell. Device according to any one of Claims 1 to 5, characterized in that it also comprises a high-pass filter in said processing chain, with cut-off frequency f₀ less than f₁. Device according to claim 6 characterized in that the slope of the transfer characteristic of said high pass filter is + 6dB / octave. Device according to claim 1 characterized in that said sensor (10) of the derivative type is a passive sensor. Device according to either of Claims 1 and 6, characterized in that the said low frequency f₁ is of the order of 100 kHz and the said frequency f l'ordre of the order of 10 MHz. Device according to either of Claims 1 and 2, characterized in that the said compensation means comprise at least one broadband amplifier and / or at least one transistor. Use of the device according to any one of the preceding claims for processing signals from an electric field, magnetic field, current and / or surface charge sensor.

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